1. Field of the Invention
The present invention relates to a transmitting system for a small-sized vehicle, in which a crankshaft of an engine and an input shaft of a multi-stage transmission are connected to each other through a fluid transmitting means including a pump impeller connected to the engine, and a turbine impeller connected to the multi-stage transmission, i.e., through a torque converter or a fluid coupling.
2. Description of the Related Art
Such transmitting system for small-sized vehicles is already known, as disclosed in, for example, Japanese Patent Application Laid-open No.57-69163.
In such known transmitting system, as disclosed in the above Publication, the crankshaft of the engine and the input shaft of the multi-stage transmission are connected to each other only through the torque converter, so that a torque shock generated at the time of starting the vehicle or during shifting is absorbed by a slipping action of the torque converter.
However, the known transmitting system suffers from the following drawbacks: The torque converter or the fluid coupling has a slipping function, but performs the transmission of a torque to certain degree, as long as power is input from the engine to the torque converter or the fluid coupling. Therefore, in the known system, at the time of starting the vehicle in which the transmission is switched over from a neutral position to a low or first-speed position, a creep phenomenon is produced in which power is transmitted to a driven wheel of the vehicle to certain degree, even if the engine is in an idling state. During traveling of the vehicle, the friction always occurs in switching and sliding portions of the transmission due to the transmitted torque. For this reason, there are inconveniences that the resistance to the switching of the transmission is large, and a large shifting load is required.
Accordingly, it is an object of the present invention to provide a transmitting system for a small-sized vehicle above-described, wherein the creep phenomenon is eliminated, and the shifting operation of the transmission can be carried out lightly, and moreover, during cruising of the vehicle, the slipping of the fluid transmitting means is inhibited to enhance the transmitting efficiency.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a transmitting system for a small-sized vehicle in which a crankshaft of an engine and an input shaft of a multi-stage transmission are connected to each other through a fluid transmitting means including a pump impeller connected to the engine, and a turbine impeller connected to the multi-stage transmission, wherein the transmitting system includes a shifting clutch which is interposed between the crankshaft of the engine and the input shaft of the multi-stage transmission, the shifting clutch being in a series relation to the fluid transmitting means, and a lock-up clutch which is interposed between the pump impeller and the turbine impeller of the fluid transmitting means, the lock-up clutch being capable of connecting both the impellers directly to each other.
The fluid transmitting means corresponds to a torque converter T in each of embodiments of the present invention which will be described hereinafter.
With the first feature, during idling of the engine, the transmitting of power to the shifting clutch and the like can be cut off by controlling the shifting clutch to its OFF state irrespective of the presence of the fluid transmitting means, even in a low or first-speed position of the transmission, thereby preventing the creep phenomenon. During shifting, the transmission can be brought into an unloaded state irrespective of the presence of the fluid transmitting means by first controlling the shifting clutch to its OFF state, thereby conducting the shifting lightly without generation of a torque shock.
Moreover, during cruising of the vehicle, if the lock-up clutch is controlled to its ON state, the pump impeller and the turbine impeller are connected directly to each other and hence, the slipping between both the impellers can be eliminated to prevent a loss of power.
According to a second aspect and feature of the present invention, in addition to the first feature, the lock-up clutch comprises a pump extension connected to the pump impeller and surrounding the turbine impeller, a pressure receiving plate coupled to a tip end of the pump extension to define, within the pump extension, a hydraulic pressure chamber communicating with an oil chamber defined between the pump impeller and the turbine impeller, a pressing plate opposed to the pressure receiving plate and biased toward the pressure receiving plate by a hydraulic pressure in the hydraulic pressure chamber, an annular friction clutch plate interposed between the pressure receiving plate and the pressing plate and connected to the turbine impeller, first and second valve bores provided in the pressing plate and the pressure receiving plate on the side of an inner periphery of the friction clutch plate, respectively, a control valve provided in the pressing plate to close the first valve bore, a control rod which is received in the first and second valve bores and movable between a retracted position in which the control rod causes the inner periphery of the friction clutch plate to be open outside the second valve bore, while permitting the closing of the control valve, and an advanced position in which the control rod causes the control valve to be open to permit the inner periphery of the friction clutch plate to communicate with the hydraulic pressure chamber, while closing the second valve bore, and an operating means for operating the control rod.
The operating means corresponds to a lock-up clutch operating shaft 86 in a first embodiment of the present invention which will be described hereinafter.
With the second feature, if the control rod is operated to the retracted position, the pressing plate can clamp the friction clutch plate between the pressing plate and the pressure receiving plate under the action of a hydraulic pressure transmitted from the fluid transmitting means to the hydraulic pressure chamber, whereby the lock-up clutch can be brought into its ON state. If the control rod is operated to the advanced position, the hydraulic pressure in the hydraulic pressure chamber can be applied to opposite sides of the pressing plate to eliminate the clamping force to the friction clutch plate, whereby the lock-up clutch can be brought into its OFF state. In this OFF state, the control rod closes the second valve bore and hence, the useless leakage of the hydraulic pressure from the hydraulic pressure chamber can be prevented.
According to a third aspect and feature of the present invention, in addition to the first or second feature, a one-way clutch is interposed between the crankshaft and the turbine impeller and brought into its ON state, when the turbine impeller receives a reverse load torque.
With the third feature, at the time of an engine brake during traveling of the vehicle, the one-way clutch is brought into its ON state by application of the reverse load torque to the turbine impeller. Therefore, the turbine impeller and the crankshaft are connected directly to each other, and the reverse load torque is transmitted to the crankshaft without via the fluid transmitting means and thus, a good engine brake effect can be provided.
According to a fourth aspect and feature of the present invention, in addition to the first feature, the lock-up clutch is constructed such that it depends on the rotational speed of the pump impeller and it automatically operates, when the rotational speed of the pump impeller becomes equal to or higher than a predetermined value.
With the fourth feature, when the rotational speed of the pump impeller becomes equal to or higher than the predetermined value, the pump impeller and the turbine impeller of the fluid transmitting means can be automatically connected directly to each other.
According to a fifth aspect and feature of the present invention, in addition to the fourth feature, the lock-up clutch comprises a pump extension connected to the pump impeller and surrounding the turbine impeller, a pressure receiving plate coupled to a tip end of the pump extension to define, within the pump extension, a hydraulic pressure chamber communicating with an oil chamber defined between the pump impeller and the turbine impeller, a pressing plate opposed to the pressure receiving plate for advancing and retracting movements, an annular friction clutch plate interposed between the pressure receiving plate and the pressing plate and connected to the turbine impeller, a return spring for biasing the pressing plate in a direction to be retracted relative to the pressure receiving plate, and an escape bore which permits the communication between the inside and outside of the pressure receiving plate on an inner peripheral side of the friction clutch plate, wherein when the rotational speed of the pump impeller becomes equal to or higher than the predetermined value, the pressing plate clamps the friction clutch plate in cooperation with the pressure receiving plate under the action of a centrifugal hydraulic pressure in the hydraulic pressure chamber which is raised in accordance with the rotational speed of the pump impeller.
With the fifth feature, the automatic control of the lock-up clutch depending on the rotational speed of the pump impeller can be conducted easily.
According to a sixth aspect and feature of the present invention, in addition to the first feature, the lock-up clutch is constructed such that it depends on the rotational speed of the turbine impeller and it operates automatically when the rotational speed of the turbine impeller becomes equal to or higher than a predetermined value.
With the sixth feature, when the rotational speed of the turbine impeller becomes equal to or higher than the predetermined value, the pump impeller and the turbine impeller of the fluid transmitting means can be automatically connected directly to each other.
According to a seventh aspect and feature of the present invention, in addition to the sixth feature, the lock-up clutch comprises a clutch cylinder connected to the turbine impeller, a pressing piston slidably received in a cylinder bore in the clutch cylinder to define a hydraulic pressure chamber, a piston return spring for biasing the pressing piston toward the hydraulic pressure chamber, a means for introducing the oil into the hydraulic pressure chamber, and a friction engagement means provided between the clutch cylinder and the pump impeller, wherein when the rotational speed of the turbine impeller becomes equal to or higher than the predetermined value, the pressing piston operates the friction engagement means under the action of a centrifugal hydraulic pressure within the hydraulic pressure chamber which is raised in accordance with the rotational speed of the turbine impeller to connect the clutch cylinder and the pump impeller directly to each other.
The friction engagement means corresponds to driving friction clutch plates 110, driven friction clutch plates 111 and transmitting claws 112 in a third embodiment of the present invention which will be described hereinafter, and the oil introducing means corresponds to the inlet bore 117 in the third embodiment.
With the seventh feature, the automatic control of the lock-up clutch depending on the rotational speed of the turbine impeller can be carried out easily.
According to an eighth aspect and feature of the present invention, in addition to the seventh feature, the clutch cylinder is provided with an escape bore which opens an outer periphery of the hydraulic pressure chamber to the outside, and a centrifugal valve which opens the escape bore, when the rotational speed of the clutch cylinder is lower than a predetermined value, and closes the escape bore, when the rotational speed of the clutch cylinder is equal to or higher than the predetermined value.
With the eighth feature, when the rotational speed of the clutch cylinder is lower than the predetermined value, the pressure remaining in the hydraulic pressure chamber can be released promptly through the escape bore by opening of the centrifugal valve to enhance the turning-off performance of the lock-up clutch, and a foreign matter such as a cut powder within the hydraulic pressure chamber can be discharged through the escape bore along with the oil. When the rotational speed of the clutch cylinder is equal to or higher than the predetermined value, the rising of the hydraulic pressure in the hydraulic pressure chamber can be conducted by closing of the centrifugal valve, and the operation of the lock-up clutch cannot be impeded.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the accompanying drawings.